The conventional principles and apparatus for packed-bed chromatography are well-established. The present invention is concerned with issues arising in commercial-scale preparative chromatography, where columns are often very large and any one or more of the particulate packing medium, the product to be separated and the time taken up in arranging the running of the procedure is/are of very high value.
It is well known that a packed column has to be continuously, uniformly and entirely filled with the relevant medium under an appropriate degree of compression of its particles.
Conventional column packing, an operation requiring great care and experience, involves removing the top plate or “cell” of the column and pouring in a slurry of the relevant medium in a liquid carrier. More recently the use of a packing port has become favoured because it obviates taking the lid off. Various kind of valved ports have been proposed for this; see for example GB-A-2258415, WO 96/10451 and WO 99/64130. The column generally has upper and lower restricted-permeability elements—mesh or sinter layers—to retain the media particles, and the packing port provides communication directly into the bed space past i.e. penetrating one or both of these restricted-permeability layers. To pack, typically the column is filled with liquid and the medium slurry pumped in through the packing port at one end, liquid carrier leaving the column via the permeable element at the other. The particulate medium is retained and gradually accumulates until the column is full. The accumulating bed is compressed by the controlled pressure from the pumped liquid and—in the usual case when packing from the top—also by the weight of the upper part of the bed. There is a subtle, continuous variation in the conditions experienced by the medium. A common procedure is for the operator to continue pumping until the column is essentially full, whereupon the pump usually cuts out spontaneously. As the liquid flow pressure is relieved, the packed bed then “relaxes” to fill the column with a more uniform compression profile over its length.
Even with packing ports, the packing of chromatography columns is a skilled job requiring training and experience. A packing nozzle helps to achieve consistent results, but only experience and time-consuming testing of trial packs can indicate the optimal slurry concentrations and pump pressure profiles for a given medium in a given column. Since many columns are of steel the operator can have very little idea of what is happening inside.